No account required, no fees. They make money from affiliate/commission links, presumably.
Cell phone and ISP plan comparison: whistleout.com Can choose many details about phone and plan & compare.
Textbook/regular book price comparison: gettextbooks.com Can search by author, ISBN, etc. Sorted by price, including new and used on many sites. Shows shipping cost. I always use this when buying books.
I wish there was something like this for groceries. I'm annoyed with flipp showing you the highest price you've ever seen for X just because it's "in the sale ad" and in real life you see two perfectly fungible products, right next to each other on the shelf, probably from the same factory but with different brands, and the unit price for one will be per oz but the other will be per lbs or per serving or per package.
My local grocery chain "Giant" has what they call their "Finest" generic brand, but we always call them "Fine-Assed!" because they are often as good or better for less money than the name brand next to them. It involves a little trial and error. As for that Lbs to Ozs stuff, you'll have to do some calculatin'. Being familiar with basic maths is vital for living on the bottom, otherwise you might not recognize a good deal (or a miss-priced item!) when it appears.